I like your work and your display! The voice sounds pretty good too! What is the distance between LEDs on the display? I am thinking about making one similar but, I need to know how far apart to put the LEDs to make it look nice like yours.
It would be interesting to see if that could be made to work with the SimpleSDAudio library. That is now capable of up to (pseudo) 16 bit Stereo direct from 1-4 PWM pins and an SD Card adapter. The Wav shield could then be removed. I've used this library in 8 bit mono using a single pin and it sounded good enough for simple sound effects and voices. It ran some Red Dwarf and Stargate voice clips very well, just into a PC speaker input.